Existing trunked radio systems include two major types of architectures, centralized and distributed. FIG. 1 shows an example of a centralized trunked radio system having a dedicated control channel and center for mobility management. Typically, the control channel may stay in a continual-emitting state while the system terminals may reside on the control channel for listening. To work properly, terminals, after booted, need to be successfully registered on the system. For example, interphone users usually may stay on the control channel, and for each call an interphone needs to send a call request through the control channel to the system and wait for the system to allocate a traffic channel in response to the call request. The system may then notify the interphone to switch to the traffic channel for communication, and the interphone would return to the control channel when the call ends.
However, if there is a disturbance to the control channel or traffic channel of the centralized trunked radio system, the system will not advise the disturbance to the terminal users. As such, if the control channel is interfered with, the terminal would not be able to receive the system-allocated traffic channel information after sending the service call request, leading to a high dropped-call rate (DCR). On the other hand, if the system-allocated traffic channel is disturbed, then after the terminal fails to establish a call on the traffic channel, the terminal would return to the control channel to initiate a call request for a new traffic channel, resulting in a big call-setup delay.
In contrast, a distributed trunked system (DTS) does not require a control channel, but also allows different interphone units to share the system channel resources. So, when a system terminal initiates a call, the channel allocation is actually controlled by the software logic of the terminal rather than determined by the control channel. As such, in a DTS, terminals would need to scan the channels for a vacant channel and start a call on the vacant channel once the vacant channel is found. This, however, increases the system access time; on the other hand, the system provides no treatment with respect to the interference with the repeaters, which also reduces the system access performance.